Natural carbon sinks such as oceans and forests -- that suck carbon dioxide out of the atmosphere -- may soon start emitting the greenhouse gas instead, if climate change remains unchecked, scientists warn.
Ecosystems that host a carbon-dioxide rich type of soil called peat, known as peatlands, are the most efficient natural carbon sink on the planet.
When undisturbed, they store more carbon dioxide than all other vegetation types on Earth combined.
However, when they are drained and deforested, they can release nearly six per cent of global carbon dioxide emissions each year. Climate researchers are worried that many of the peatlands soaking up carbon now will soon be doing the opposite.
"Global peatlands cover only about three per cent of global land area, but hold around 30 per cent of the earth's soil organic carbon," said Qianlai Zhuang, a professor at Purdue University in the US.
Researchers looked to peatlands in the Peruvian Amazon to understand whether a large amount of peat carbon would be released under a warmer climate.
According to an earth systems model spanning from 12,000 years ago to 2100 AD, this relatively small basin could lose up to 500 million tonnes of carbon by the end of this century.
That is about five per cent of current global annual fossil fuel carbon emissions, or 10 per cent of US emissions, being spit back out into the atmosphere.
By most estimates, South America will become both warmer and wetter by the end of the century.
The findings, published in the journal Proceedings of the National Academy of Sciences, show that higher temperatures lead to more peat carbon loss, while increased precipitation slightly enhances the build-up of peat carbon over long timescales.
Together, this is likely to increase carbon loss from peatlands to the atmosphere.
"If the area we looked at could represent the whole Amazonia or tropical peatlands, the loss of peat carbon to the atmosphere under future climate scenarios should be of great concern to our society," Zhuang said.
"Agricultural intensification and increasing land-use disturbances, such as forest fires, threaten the persistence of peat carbon stocks," he said.
"These peatland ecosystems may turn into carbon sources instead of sinks unless necessary actions are taken," he added.
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